Simple Custom App Question

I keep seeing mixed information about this very simple inquiry.

I’m looking to build a custom app for a store that has an accessible UI on the admin side for the shop owner. Said shop owner does not want this app publicly available.

Do I have to be a Shopify Partner to make this? When I run shopify app dev it keeps asking about a “Shopify Partners organization”. Is this functionality gatekept and if not then can someone please point me in a direction that isn’t Shopify Partners related?

The answer I’ve come to is that you have to create and use a Shopify Partner account to create an embedded custom app. Seems to me like reaching around your elbow to scratch your ass but c’est la vie.